This invention relates to ultraviolet lamp assemblies, particularly useful for the curing of photopolymerizable materials, and more specifically relates to a novel ultraviolet lamp assembly in which a water jacket directly surrounds the lamp in order to cool the lamp. A reflective coating is formed on a wall of the water jacket in order to direct ultraviolet radiation toward a focused region to one side of the lamp or toward a substrate.
The use of ultraviolet lamps is well known for curing photopolymerizable materials, such as photopolymerizable ink. Such ink, printed on a suitable substrate, is substantially instantaneously cured upon exposure to intense ultraviolet radiation. Ultraviolet curing ovens for producing intense ultraviolet light for this purpose are shown, for example, in U.S. Pat. No. 3,733,709 to Bassemir et al, U.S. Pat. No. 3,745,307 to Peek et al, U.S. Pat. No. 3,826,014 to Helding, and U.S. Pat. No. 3,840,999 to Whelan, each of which is assigned to the assignee of the present invention.
The operation of conventional ultraviolet lamps generates substantial heat as well as the ultraviolet radiation which is used for the curing of the photopolymerizable materials.
The heat or non-ultraviolet energy which is produced by the lamp must be efficiently removed from the lamp region to prevent damage to the lamp apparatus and to the substrate carrying the photopolymerizable material to be cured. Thus, extremely bulky apparatus is now in use which utilizes water-cooling conduits or air channels embedded in large heat sinks adjacent the lamp structure in order to remove the heat from the lamp as efficiently as possible. Presently existing ultraviolet lamp apparatus also produces extremely large quantities of ozone and the ozone must be removed efficiently from the equipment, thereby requiring relatively large air evacuation and handling ducts for sweeping ozone across the lamps and around the lamp reflectors.
The intense heat produced by the lamps is especially damaging to paper webs or sheets being carried through the curing oven when the sheets slow down or are stopped; therefore, it is common practice to reduce lamp power and to provide shutters which can be moved between the lamps and the web in order to block radiation which might fall on the web when it is stopped and to absorb the heat produced by the lamps so that the web or sheets being transported through the oven are not charred or burned. These shutters are usually relatively massive structures and are frequently provided with water-cooling conduits to conduct away the heat produced in the shutters by the adjacent lamp structures. The lamp power is not turned off when the web is temporarily stopped since the lamp would have to cool down for several minutes before it can be reignited.